The present invention relates to the maintenance of helicopters. In particular, the present invention relates to a blade positioning system used for the installation of helicopter rotor blades.
Helicopters are useful for a broad range of short-range and medium-range flight missions due to their versatility, load-carrying capacity, and ability to take off and land in a vertical path. This VTOL (“Vertical Take-Off and Landing”) capability is particularly useful for maritime flight operations where the available space is strictly limited. It is also useful in field operations where suitable landing strips for other aircraft may not be readily available.
The flight capability of a typical helicopter is provided by at least one main rotor assembly having a plurality of rotor blades, with an overall structural envelope that typically extends far beyond the helicopter body. This results in the need for a large amount of storage space per helicopter, whether it is stored in a hangar, stowed below-decks in an aircraft carrier or other vessel, or stored in an aircraft for transport to a location in the field. Stimulated by the strategic and tactical considerations of military as well as civilian use, helicopter designers have taken various approaches to reducing the space requirements for helicopter storage during routine transport and stowage, while not compromising the need for rapid deployment.
One approach is a main rotor assembly with removable rotor blades which can be stacked for storage, greatly reducing the structural envelope of the helicopter. With the rotor blades removed, several helicopters can be stored in the space required for one fully-deployed helicopter. However, main rotor assemblies may be complex in design, and once removed, reinstallation of the blades is labor-intensive and time-consuming. Many helicopter blades have bifurcated ends that must be precisely aligned with corresponding hub structures when the blades are reattached to the main rotor assembly. The sheer weight and size of the blades makes this process difficult for the involved personnel.
Another approach is the type of blades known as “folding” blades. Both automated and manual folding blade assemblies are available. Automated assemblies typically require extensive modifications to the main rotor assembly as well as software to regulate the blade folding operations, all of which increases the complexity and cost of the helicopter. Automated blade folding assemblies may also have higher maintenance requirements and decreased reliability when compared to conventional, fixed-blade rotor assemblies. Manual folding blade assemblies require fewer modifications to the main rotor assembly. In a typical manual folding blade assembly, the individual rotor blades are attached to a rotor hub by blade pins. In one type of rotor assembly with folding blades, removal of one of a pair of blade pins allows the blade to pivot around the remaining pin into a folded position. The structural envelope of the rotor assembly is more compact with the blades in the folded positions than when the blades are deployed for use, resulting in correspondingly less need for storage space.
Correct blade alignment is crucial for both flight safety and accurate navigation. Thus, whenever helicopter blades are disassembled, there are concerns about the proper alignment of the blades when they are re-deployed for use. Whether the blades are folded or removed totally, they must be properly realigned with the hub before the blade pins can be installed. Because of the size of the main rotor blades, even small displacements such as are easily induced by wind gusts, inaccuracies in aligning the blades, etc can lead to compromised safety and navigational errors. A main rotor blade can easily be 20 feet long and weigh over 150 pounds with a center of gravity 10 feet out from the rotor hub, making it difficult for service personnel to position and align the blades correctly.
Mechanisms for servicing helicopters, including a variety of blade alignment mechanisms are available. By way of example, Muylaert (U.S. Pat. No. 6,213,712) discloses a helicopter blade positioning mechanism for foldable rotor blades. The system includes a connection which can be attached to the pitch control housing and which can pivot relative to the housing with two degrees of freedom, a rotor blade clamp which can be attached to a rotor blade, and a clamp positioner which positions the rotor blade clamp at a distance from the connection after removal of one of the blade pins. The mechanism permits the rotor blade to pivot about the remaining blade pin, allowing controlled folding of the main rotor blade while the blade remains attached to the pitch control housing.
Ide, et al (U.S. Pat. No. 5,946,981) describe an automatic pitch link adjuster for helicopter rotor blades. The adjuster includes a diamond-shaped frame that carries a worm and a worm wheel mounted to a turnbuckle shaft, and an electric motor coupled to the worm shaft through a spline. The pitch link is adjusted by operating the motor to rotate the shafts with respect to each other.
Noehren, et al. (U.S. Pat. No. 5,263,821) provide a mid-beam jointed reconfigurable bearingless main rotor assembly that facilitates removal or folding or the main rotor blade of a helicopter. The torque tube subassemblies include access panels (for blade removal) and removable splice tubes (for blade folding).
Costanzo, et al. (U.S. Pat. No. 5,149,013) disclose a retractable helicopter rotor where the connection between the rotor support system and the fuselage is a single interface between overlapping circumferentially extending flanges joined together by compression-loaded bolts. The rotor, swashplate, and pitch change rods are moved as a unit between an operational position and a retracted stowage position, without requiring disconnection and reconnection of the pitch change rods.
Covington, et al. (U.S. Pat. No. 4,252,504) show a helicopter blade folding system with blade pins which are locked in place by a latch plate. Each pin has an annular groove that is mated to a corresponding aperture in the latch plate.
Mayerjak (U.S. Pat. No. 4,156,583) provides a hub assembly for an articulated rotor system that includes three plates centrally secured to the shaft. The assembly supports blade retention assemblies that are equally spaced about the rotor shaft.
Alignment tools are used with other apparatus where precise alignment of components is desired. For example, Allyn, et al. (U.S. Pat. No. 6,371,209) disclose a casing installation and removal adapter for downhole well drilling apparatus. The adapter is mounted on the lower end of a pneumatic hammer drill, and couples the drill to a pipe string maintaining a movable part of the drill in an operative condition. This enables the drill to operate while rotational torque and upward directed force are simultaneously applied during removal of a casing from a downhole position. The adapter includes a cylindrical main portion threaded with a male hammer chuck thread which mates with the female hammer chuck thread within the lower end of a hammer drill barrel. A reduced-diameter cylindrical portion engages the lower end of a hammer drill and operates to maintain the piston in the hammer drill barrel.
Bocking, et al (U.S. Pat. No. 4,681,175) show an auto-coupling tool for drill-pipes having a body portion with a female-threaded adapter at one end and a tapered, multi-intertwined-spiral bit portion at the other end. The tool is used to retrieve broken drill pipes.
Esperandieu, et al (U.S. Pat. No. 5,909,935) provide a device used for guiding, driving, and locking a slot-in module in a cabinet (the module contains electrical or electronic equipment whose circuitry is to be connected to the circuitry of the cabinet). Their device includes a slideway and a slide fixed to the cabinet and the module, respectively, for guiding the module into its proper position.
Bittner (U.S. Pat. No. 5,813,300) shows a precision center with interchangeable double-arcuate floating collet, used for mounting a workpiece for precision machining. This device includes a modified head center, a drive assembly mounted within the head center and mechanically coupled to an actuating assembly, and a double-arcuate floating collet.
Williams, et al (U.S. Pat. No. 4,890,947) disclose a mounting adapter for a centrifuge rotor. The adapter includes a spud member with an internal chamber defined by a locking surface and a lifting surface, with a threaded access bore and a mounting bore (see Fig). A connecting member has a head confined within the chamber and a shank extending into the mounting bore, and is rotatable by a tool extended through the access bore.
Deutsch (U.S. Pat. No. 4,488,842) shows an improved nose member for an expandable bushing type locking assembly of the type which includes a handle with camming means at one end to operate the bushings. The improvement consists of a nose cone on the free end of the locking pin, positioned so as to overlie the adjusting nut. The tapered nose cone guides the pin into the parts to be assembled.
Battrick (U.S. Pat. No. 4,237,754) provides a universal spud wrench has a tubular shaft with four perpendicularly oriented sloped surfaces that form four longitudinal slots, with aligned extensions (with different diameters) adjacent the slots and a cross-wise shaft to facilitate turning.
Fenton (U.S. Pat. No. 4,191,228) discloses a tool which includes a drive member (such as a lever arm or shaft), a driven member (the object to be turned), and a torque transfer assembly having a male portion formed on one of the drive and driven members and a female portion on the other member. The drive member can turn the driven member in only one direction; it disengages when turned in the opposite direction.
Despite the availability of alignment tools and servicing tools, there remains a need for a simple, reliable system for the efficient installation of helicopter rotor blades. An ideal system would result in correctly and reproducibly aligned blades, and be straightforward to implement regardless of operating conditions. Further, it would reduce the amount of wear and tear that the alignment process exposes blade pins to when connecting blades to main rotor hubs.